In recent years, static random access memory (SRAM) devices have been fabricated having cell gate patterns sequentially stacked on an active region of a semiconductor substrate. Current in the device may be increased when the cell gate patterns are arranged in a three-dimensional manner on the semiconductor substrate, compared with a two-dimensional arrangement. In addition, sequentially stacking the cell gate patterns may provide increased device density for a given set of design rules.
However, there may be a structural limit in applying a silicide process to a peripheral circuit region of an SRAM device. This is because the cell gate patterns of an SRAM device may be disposed vertically in the cell array region, while peripheral gate patterns are disposed laterally in the peripheral circuit region. Thus, when a silicide process is performed on the peripheral gate patterns and the semiconductor substrate near the peripheral gate patterns, the silicide process may cause metal contamination in the cell gate patterns, which may degrade the electrical characteristics of the SRAM device.
U.S. Pat. No. 6,287,913 to Paul D. Agnello et al. (the '913 patent) discloses a double polysilicon process for providing both logic and memory circuits/devices in a single chip.
According to the '913 patent, a double polysilicon process includes forming a memory gate stack on a memory region. After the gate stack is formed, a logic gate stack is formed on a logic region. A silicide process is then performed on the logic region to form cobalt (Co) or titanium (Ti) silicides on a top surface of the logic gate stack and the semiconductor substrate near the logic gate stack.
However, in the polysilicon process, the memory stack and the logic gate stack are not formed at the same time. Accordingly, use of a double polysilicon process may require a lengthy fabrication process and/or may increase the cost of fabricating a semiconductor chip.